In the field of mine roof bolting, many methods and types of anchors are presently in use. They fall into several general categories and include a mechanical system, a combination mechanical and resin system, a resin point anchor system, a fully grouted tension system and a non-tension fully grouted system. The use of any particular system is predicated upon a number of considerations including the integrity of the strata at the anchoring horizon, the condition of the roof being supported, etc.
In mines where the roof is very difficult to support, there is a trend toward the use of an anchor which will withstand much higher bolt tension loads than was thought practical and necessary in the past. This increase in the tension and roof bolting has resulted in the most marked improvement in roof control since the beginning of roof bolting in mines. The new anchors, called "point anchors" are usually encapsulated in resin as they are tightened. The resin adds to the stability of the anchor, but its main advantge is in maintaining the initial installed tension.
For effecting maximum tension loads, it is also desirable to drill small bore holes for roof bolts, but to use the largest diameter roof bolt possible that can be anchored in the hole. Up to the present time, however, the size of the roof bolts has been necessarily limited due to space limitations created by conventional expansion shells.